The present invention relates to an absorbent for treating a gas containing at least one compound of volatile inorganic hydrides, such as silane, diborane, hydrogen selenide, germane, arsine, phosphine, stibine and the like, volatile inorganic halogenides, such as dichlorosilane, trichlorosilane, silicontetrafluoride, borontrichloride, arsenic trichloride and the like, and organometallic compounds, such as trimethylaluminum, trimethylgallium, and the like. The present invention further relates to a process of toxo-cleaning such compounds in gases with the same absorbent.
In the manufacture of integrated circuits, large-scale integrated circuits and the like in the semiconductor industry, volatile inorganic hydrides, volatile inorganic halogenides and organometallic compounds are used in a gaseous or a liquid state for vapour growth deposition, etching, doping and diffusion. Those materials have strong flammability or strong toxicity. For example, silane is of a nature such that even if a trace amount of silane leaks into the air, it burns with a strong reaction with oxygen. It is well known that diborane, hydrogen selenide and germane have strong toxicities. Therefore great caution is necessary to treat it. When waste gases which are exhausted from the above-described semiconductor manufacturing processes contain such toxic components in nitrogen or hydrogen gas as a base gas, safety treatment thereof is required. Heretofore, various processes have been proposed for removing the toxic components. A widely adopted process is wet absorption process, in which a waste gas is brought into countercurrent contact with an aqueous solution of sodium hydroxide, whereby toxic components in the waste gas are absorbed into the sodium hydroxide solution for removal thereof. Although this wet absorption process is advantageous in that waste gases can be processed with relatively cheap sodium hydroxide, it requires a gas treating unit in a relatively large scale or a large amount of sodium hydroxide in order to sufficiently remove certain kinds of toxic gases. Since the waste solution after the absorption of toxic components is an aqueous alkaline solution, wet absorption process has disadvantages in that the handling of the waste solution is inconvenient, in that the disposal thereof is relatively difficult, and in that the cost in transportation of the waste solution for disposal is rather high. The greater the amount of the solution to be disposed increases, the larger such disadvantages become. In another process utilizing the flammability of volatile inorganic hydrides, the toxic materials are removed by bringing them into contact with air for combustion in a combustion chamber having water stored therein. Although such a process may be applied to specific volatile inorganic hydrides such as silane, it can produce an explosion hazard, and further it is not applicable to waste gases containing various kinds of toxic components as exhausted from recent semiconductor manufacturing processes.